This project proposes to continue an investigation of stereospecificity in biological reactions, particularly the ability of enzymes to discriminate between like groups attached to a prochiral center. Six specific goals are outlined for the renewal period: 1. To determine the absolute specificity of the hydroxymethyl transferase reaction in hydroxymethylserine. 2. To elucidate the stereochemistry of hydrogen migration in the ethanolamine ammonia-lyase reaction. 3. To investigate the stereospecificity of hydrogen loss from the prochiral methylene of isoleucine during metabolism to tiglic acid. 4. To investigate the stereospecificity of hydroxylation during enzymatic conversion of phenylalanine to mandelonitrile in the millipede. 5. To study the stereospecificity of enzymatic reactions at prochiral carbons during microbial degradation of camphor. 6. To investigate enzymatic differentiation between the diastereotopic methyls of valine during pantothenic acid biosynthesis.